UV Maps Angled & Stretched Incorrectly
It's generally very unusual to have a non-square UV map, and it's also pretty unusual to have a UV map that isn't based on powers of two. I don't know how you've come up with those numbers but you're almost certainly best off sticking to 128x128 if that's the rough size of texture you're looking at.

The non-square UV map is the reason you're having this problem, and if you really need it, there is a quick fix:

Select everything on the UV map and scale it by the ratio of the map itself. So in your case, S to scale, Y to constrain to the Y-axis, and then type 0.75 (102/136) as the amount and it will correct the distortion.